With the increasing demands of energy saving, environmental protection and sewage discharge at home and abroad, the traditional pretreatment materials containing P, MN, ni and other heavy metal pollutants are gradually prohibited by local laws and regulations, the new green phosphorus-free conversion membrane technology gradually mature and rapid development, the process can completely do not use P, MN, Ni, nitrite and other harmful substances, the current main zirconium salt pretreatment process, silane pretreatment process. Zirconium On the same substrate, the nano-scale film and the ternary phosphating film formed by phosphorus-free pretreatment have considerable corrosion resistance, Zirconium at present, the new planning coating plant in China usually takes into account the phosphorus-free pretreatment process, and the traditional phosphating production line is beginning to switch to phosphorus-free production line gradually. Zirconium In this paper, the application of zirconium salt process in Zirconium phosphorus-free pretreatment and the traditional phosphating switching to zirconium salts were analyzed.
Zirconium Salt Conversion Film is a zirconium (H2ZRF) as the main body, metal substrate in the zirconium salt acidic solution in the electrochemical reaction, forming a layer of nanometer inorganic film
Ternary phosphating film thickness in $number μm, Zirconium zirconium salt conversion film thickness in 20, scanning electron microscope (SEM) observation, the zirconium film is more dense than ordinary phosphating film (Fig. 1, fig. 2). There is a gap between the phosphate film membrane, and the corrosion of the membrane is started and gradually spreads to the periphery. The film is dense, Zirconium the film has no clearance between the membranes, so it is not easy to dissolve the film, so it has excellent corrosion resistance.
Pre-ZR pretreatment and ternary phosphating pretreatment can deal with cold rolled sheet (SPC), galvanized Plate (GA), aluminum plate and other substrates, Zirconium but there is a slight difference in the anti-corrosion performance after treatment. The experiment used cold rolled sheet, galvanized sheet, aluminum sheet as the base material, respectively for the ternary phosphating pretreatment and zirconium salt pretreatment and supporting electrophoresis, after electrophoresis on the aluminum plate and cold-rolled plate 960h SST (neutral salt spray) test, Zirconium galvanized plate for 26 cycles of CCT (cyclic corrosion) test, fig. 3, 5, 7 for the same pretreatment plant ternary phosphating (zinc system) and zirconium pretreatment (Zirconium series) supporting different electrophoresis paint, fig 4, 6, 8 for different manufacturers of the former treatment matching the same electrophoresis paint, Zirconium The results of the experiment are as follows.
The comparison test results show that the corrosion resistance of galvanized sheet is similar to that after phosphating treatment, but there are differences in the treatment of aluminum plate and cold-rolled plate. After phosphating treatment, the corrosion resistance of aluminum plate Zirconium is worse than that of zirconium, and the maximum corrosion width is above 2mm, and the aluminum plate treated with zirconium has almost no corrosion, and the main aluminum is treated by ordinary phosphating. There can be no film or membrane precipitation phenomenon, can not reach the anti-corrosion effect, so phosphating in the treatment of aluminum materials in the treatment of the content of F ions to adjust, increase F-ion on the corrosion of the plate, can meet the requirements of anti-corrosion. The corrosion resistance of cold-rolled plate after zirconium treatment is weaker than that of phosphating treatment, the maximum corrosion width is 4mm, the film is thin and the corrosion resistance is poor after electrophoresis.